(1) Field of the Invention
The invention relates to a method of fabricating semiconductor structures, and more particularly, to a method to form a color image sensor device while protecting the bonding pad structure in the manufacture of an integrated circuit device.
(2) Description of the Prior Art
Color image sensors are an important device in the art of integrated circuits. A color image sensor combines cell electrodes with color filtering elements. In a typical color image sensor cell, the cell electrodes comprise a patterned metal layer. The color filter elements are formed overlying the cell electrodes with a transparent layer therebetween. The color filter elements permit light transmission of particular wavelengths, for example, green, red and blue light. The color filter elements each comprise a patterned photosensitive, organic photoresist material. Bonding pad structures are used in the color image sensor integrated circuit to provide electrical connectivity outside the circuit. Unfortunately, it is found that the processes used to pattern the color filter elements can negatively effect the performance of the bonding pad structures.
Referring now to FIG. 1, a prior art color image sensor integrated circuit die 10 is illustrated. The integrated circuit die 10 is fabricated on a semiconductor substrate. A color image sensor array is formed in the interior of the die 10. The array is formed of a large matrix of individual cells 14. Bonding pad structures 18 are formed on the periphery of the die 10 to provide of-chip connectivity.
Referring now to FIG. 2, a cross section of a simplified, color image sensor cell is shown. The semiconductor substrate 30 typically comprises monocrystalline silicon. Two types of metal structures 34 and 38 are formed overlying the semiconductor substrate 30. Cell electrodes 34 and bonding pad structures 38 are formed by patterning a metal layer. As shown in the top view of the circuit die, the cell electrodes 34 and the bonding pad structures 38 are typically formed in two different regions of the circuit. A passivation layer 39 and a transparent planarization layer 42 are deposited overlying the cell electrodes 34 and bonding pad structures 38. A photosensitive, organic photoresist layer 46 is applied overlying the transparent planarization layer 42.
Referring now to FIG. 3, the photoresist layer 46 is patterned to form a color element 46 such as, for example, a green pixel. The photoresist layer 46 is patterned using a photolithographic mask exposure and development sequence. Of particular importance, the developer solution can penetrate 50 the planarization layer 42 and interact with the bonding pad structures 38. The developer can cause damage that is commonly called staining. Bonding pad staining causes yield and reliability problem. Wire bondability, as measured by bonding strength, is reduced by the staining caused by the color filter developer.
Several prior art inventions describe methods to form bonding pads. U.S. Pat. No. 5,719,087 to Chen et al teaches a method to prevent electrochemical damage to bonding pad surfaces during a passivation etch. A capping layer of PECVD oxide is deposited overlying the bonding pad prior to the passivation layer deposition. U.S. Pat. No. 5,807,787 to Fu et al discloses a method to reduce pad to pad leakage current. After polyimide layer patterning and plasma ashing, a thermal treatment is performed on the passivation layer to reduce leakage current. U.S. Pat. No. 5,565,378 to Harada et al teaches a method to form a passive state film on the surface of a bonding pad. The wafer is immersed in an ozone-containing solution to thereby form an aluminum oxide film that does not contain pinholes. The passive state film protects the bonding pad from water intrusion. U.S. Pat. No. 5,508,229 to Baker discloses a method to form solder bumps in an integrated circuit device. Solder is deposited through a mask onto a metal layer. The metal layer not covered by the solder is then etched away. An etching solution comprising phosphoric acid, de-ionized water, acetic acid, and hydrogen peroxide is used.
A principal object of the present invention is to provide an effective and very manufacturable method to form color image sensor cells and bonding pad structures in the manufacture of an integrated circuit device.
A further object of the present invention is to form a metal oxide layer overlying the bonding pads structures to protect the bonding pad from damage due to the color filter element developer.
A yet further object of the present invention is to. form the metal oxide layer overlying the bonding pads by dipping the integrated circuit wafer into a hydrogen peroxide solution.
Another further object of present invention is to improve the bondability of bonding pads in an integrated circuit device containing color filter elements.
Another further object of the present invention is to provide a method that will work with bonding pads comprising any of aluminum, aluminum alloys, and copper.
In accordance with the objects of this invention, a method to form color image sensor cells without damaging bonding pads in the manufacture of an integrated circuit device is achieved. The method comprises, first, forming cell electrodes and bonding pads on a semiconductor substrate. A passivation layer is formed overlying the cell electrodes but exposing the top surface of the bonding pads. The semiconductor substrate is then dipped in a hydrogen peroxide solution to thereby form a metal oxide layer overlying the bonding pads. A first transparent planarization layer is deposited overlying the passivation layer and the metal oxide layer. A color filter photoresist layer is deposited overlying the first transparent planarization layer. The color filter photoresist layer is patterned to form color filter elements to complete the color image sensor cells in the manufacture of the integrated circuit device. The presence of the metal oxide layer prevents damage to the bonding pads from an alkaline developer.